Definition
A preliminary injunction is an injunction that may be granted before or during trial, with the goal of preserving the status quo before final judgment.
Overview
To get a preliminary injunction, a party must show that they will suffer irreparable harm unless the injunction is issued. Preliminary injunctions may only be issued after a hearing. When determining whether to grant preliminary injunctions, judges consider the extent of the irreparable harm, each party's likelihood of prevailing at trial, and any other public or private interests implicated by the injunction. Parties may appeal the judge's decisions on whether to award a preliminary injunction.
In Winter v. Natural Resources Defense Council, Inc, 555 U.S. 7 (2008), the Supreme Court described the balancing test for whether a preliminary injunction is appropriate. A court needs to examine whether the plaintiff is likely to succeed on the merits, whether the plaintiff is likely to suffer irreparable harm without the injunction, whether the balance of equities and hardships is in the plaintiff's favor, and whether an injunction is in the public interest.
Interlocutory Element
The judge's decision to deny the injunction would be a type of interlocutory order, and if the party seeking the injunction wishes to appeal the order, the party would make an interlocutory appeal.
Rules of Civil Procedure
In the federal courts, preliminary injunctions are governed by Rule 65 of the Federal Rules of Civil Procedure. State rules regarding preliminary injunctions vary from state to state.
Further Reading
For more on preliminary injunctions, see this American Bar Association article, this Washington and Lee Law Review article, and this University of Florida Law Review article.